Field of the Invention
The present invention relates to a method of communicating with a built-in sensor, in particular a rotational speed sensor, which supplies an output signal with successive signal pulses. In a preferred embodiment, the sensor is built into a motor vehicle in such a way that it can be supplied with a supply voltage externally via a voltage supply line.
Although applicable to any desired sensors, the present invention and the problem area on which it is based are explained using a rotational speed sensor which supplies successive logic L and H signal pulses as output signal.
The prior art discloses various rotational speed sensors which are intended to be able to detect the revolutions of a wheel. By way of example, a sensor with a gearwheel is known, in which the teeth and gaps of the gearwheel are converted into logic H=HIGH and L=LOW states, respectively. The teeth and the gaps of the gearwheel are formed as alternating magnetic north and south poles of a ring magnet. When the gearwheel is rotated, a magnetic sensor, e.g. a Hall sensor, senses the alternating sequence of north and south poles. This alternating sequence can be then converted into logic H=HIGH and L=LOW states, respectively, of a magnet signal. In the case of a prior art two-wire current interface, these states are output such that each state is assigned a specific current consumption. As a result, the two supply lines can simultaeously be used as signal output lines as well.
A rotational speed sensor with a three-wire voltage interface is likewise known. In that case, too, the three supply lines can simultaneously be used as signal output lines as well.
In the prior art sensors of that type, however, it is not readily possible to ascertain the operational reliability with which it is operating. Depending on where it is built in, it may receive a very large or a very small input signal. Monitoring the mechanical assembly would be better served by an additional signal allowing a statement about the magnitude of the sensor signal.
More generally, the sensor is, as a rule, built into the motor vehicle at an inaccessible location, so that direct communication with the associated integrated intelligent circuit is not possible. Only the supply lines of the rotational speed sensor are freely accessible after the latter has been built in.
Therefore, in the case of the known approach above, what has turned out to be disadvantageous is the fact that it is no longer possible to perform programming or interrogation for a read-out of the sensor in the built-in state.
It was proposed, therefore, that the sensor send digital output data in a specific protocol which, in a specific reserve bit, can signal that a specific input signal magnitude has been exceeded. In general, it would be desirable at the same time to output the complete information about the input signal in this way, but the protocol is relatively simple and slow for reasons of interference immunity.
The object of the invention is to provide a method of communicating with a built-in sensor which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this kind, and in which it is possible to perform programming or interrogation for a read-out of the sensor in the built-in state without the operational reliability being reduced.
With the above and other objects in view there is provided, in accordance with the invention, a method of communicating with a built-in sensor, such as a rotational speed sensor which, in a preferred embodiment may be built into a motor vehicle, the sensor receiving a supply voltage externally via a voltage supply line and outputting an output signal with successive signal pulses. The novel method comprises the steps of:
placing the sensor into a detection mode;
externally modulating the supply voltage on the voltage supply line connected to the sensor;
analyzing the modulated supply voltage received in the sensor with regard to a fulfillment of a predetermined criterion stored in the sensor; and
interpreting the received modulated supply voltage as an external communication signal if the criterion is fulfilled.
In other words, the concept underlying the present invention is found in the method steps which are carried out after the rotational speed sensor has been put into a detection mode: providing an external modulation of the supply voltage on the voltage supply line; analyzing the modulated supply voltage received in the sensor with regard to the fulfillment of a predetermined criterion stored in the sensor; and interpreting the received modulated supply voltage as an external communication signal if the criterion is fulfilled.
The novel method provides the particular advantage over the prior art solution approaches that it is possible to perform programming or interrogation for a read-out of the sensor in the built-in state without the operational reliability being reduced. In particular, it is possible to signal to the sensor the desire for a test mode which is largely insusceptible to interference.
In accordance with an added feature of the invention, the sensor outputs as its output signal a signal with successive logic L and H signal pulses.
In accordance with an additional feature of the invention, the sensor is a rotational speed sensor supplied externally via a two-wire current interface, and the method further comprises:
comparing the modulated supply voltage received in the rotational speed sensor with an associated sensor current; and
interpreting the received modulated supply voltage as an external communication signal if a negative resistance characteristic is ascertained.
In accordance with another feature of the invention, the rotational speed sensor is switched into a communication mode if a negative resistance characteristic is ascertained over a predetermined number of cycles of the sensor output signal of respective L and H signal pulses.
In accordance with a further feature of the invention, in the communication mode, each modulation of the supply voltage having a predetermined signal duration and signal magnitude is interpreted as an external communication signal.
In accordance with again an added feature of the invention, a logic xe2x80x9c1xe2x80x9d corresponds to an H pulse with ⅔ period duration and an L pulse with ⅓ period duration.
Furthermore, a logic xe2x80x9c0xe2x80x9d may be defined as corresponding to an H pulse with ⅓ period duration and an L pulse with ⅔ period duration.
In accordance with again an additional feature of the invention, in the communication mode, outputting with the rotational speed sensor communication signals on the voltage supply line to an externally accessible terminal.
In accordance with again another feature of the invention, the supply voltage is maintained substantially constant in a case of no communication.
In accordance with again a further feature of the invention, the rotational speed sensor is connected to and can be supplied externally via a three-wire voltage interface.
In accordance with yet an added feature of the invention, in the communication mode, the rotational speed sensor outputs communication signals on the voltage output line to an externally accessible terminal point.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method of communicating with a built-in sensor, in particular a rotational speed sensor, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.